This invention relates generally to a hydraulic timing mechanism to relatively displace a drive member and a driven member. More particularly the present invention concerns advancing and/or retarding the camshaft of an internal combustion engine of a vehicle relative to the engine crankshaft where the relative displacement occurs only during certain specified engine operating conditions. The standard position is maintained or returned to when the specified conditions are not met.
Thus, at lower engine temperatures, or at low vehicle speed, or when acceleration is required the timing mechanism would be in the standard position. When conditions are sufficiently changed, an alternate position is effected by the mechanism causing the relative displacement of the drive and driven members to a more efficient position.
Other timing mechanisms for relatively displacing the engine camshaft and crankshaft have been devised. For example, U.S. Pat. No. 2,159,017 to Duncan, in which hydraulic fluid pumped in proportion to engine speed displaces a piston a distance dependent on flow rate. The piston is mechanically linked to the camshaft and so the piston displacement results in a proportional relative displacement of the camshaft. Engine intake vacuum is used to modify the fluid pressure against the piston by opening an additional port and thereby decreasing the fluid pressure against the piston when intake vacuum is insufficient to overcome a spring force. In U.S. Pat. No. 2,162,243 to Brown, the axial shifting of a piston by mechanical linkage, which is independent upon fluid pressure on both sides of the piston, causes a displacement of the drive and driven members. Pressure on one side is determined by intake manifold vacuum responsive valve, and on the other side by an engine speed responsive valve. U.S. Pat. No. 2,861,557 to Stolte discloses a timing mechanism which utilizes a hydraulic linkage for the relative displacement. This mechanism utilizes a valve responsive to centrifugal force which is a function of engine speed. The valve, when engine speed increases, lessens or closes an escape port thereby increasing the pressure of fluid between the drive and driven vanes resulting in a relative displacement of said drive and driven vanes.
The above patents illustrate the need for a timing mechanism to advance and/or retard the engine camshaft with respect to the engine crankshaft under certain operating conditions. However, these inventions have not been commercially practical. The timing of the advance or retard has not been optimized because the prior art inventions have been responsive to only a limited number of engine operating conditions. When responsive to the amount of both intake manifold vacuum and engine speed, the invention as shown by the Duncan and Brown patents has been unduly complicated, expensive, subject to wear, and not adaptable for easy retrofit to an internal combustion engine. Because of these negative factors, it was prior to applicant's invention not deemed practical to make these devices responsive to other significant operating vehicles, namely engine temperature and vehicle speed (when the engine is incorporated in a vehicle). The Stolte patent attempted to obviate the problems of a timing mechanism being unduly complicated, expensive, and not adaptable for retrofit to standard engines. However, this device was still relatively expensive, subject to wear due to the constant mechanical movement, and resulted in inefficient timing, it being responsive only to engine speed (i.e., acceleration at higher speeds would be severely hampered).